1. Field of the Invention
The present invention relates to an operating device for a Venetian blind to control raising and lowering of the slats and to adjust tilting angle of the slats, more particularly to an operating device which is capable of clamping releasably the pull ropes in an effective manner and which combines the functions of controlling raising and lowering of the slats and adjusting tilting angle of the slats in a single structure.
2. Description of the Related Art
Referring to FIG. 1, a conventional Venetian blind includes an elongated housing 1, a horizontally disposed shaft 2 journalled in the housing 1, a plurality of slats 5 suspended one above another from the housing 1, a bottom rail 7 disposed below the slats 5, a plurality of pull ropes 6, each of which has a first end that passes through the housing 1 and through the slats 5 and that is mounted to the bottom rail 7, and a second end that extends out of the housing 1, a clamping unit 8 provided at one end of the housing 1 for clamping releasably the pull ropes 6, a plurality of pairs of tilting cords 4 disposed at longitudinal sides of each of the slats 5 and having top ends secured to the shaft 2 and bottom ends secured to the bottom rail 7, a plurality of suspending strings 4a disposed below each of the slats 5 to interconnect the tilting cords 4, and a tilt control unit 9 coupled to the shaft 2 for controlling tilting of the slats 5.
Referring to FIG. 2, the clamping unit 8 is shown to include a hollow seat 8a disposed in the housing 1, a stationary roller 8b and a movable roller 8c provided within the hollow seat 8a, and a retaining rod 8d for retaining the movable roller 8c to prevent removal thereof from the hollow seat 8a. The pull ropes 6 pass between the stationary roller 8b and the movable roller 8c. To lower the slats 5, the pull ropes 6 are moved leftward toward the stationary roller 8b to permit downward movement of the movable roller 8c away from the stationary roller 8b so that the pull ropes 6 are not clamped between the stationary roller 8b and the movable roller 8c. The slats 5 can thus be lowered due to the weight of the bottom rail 7. When the slats 5 are lowered to a desired position and are to be positioned thereat, the pull ropes 6 are moved rightward (as illustrated by the phantom lines of FIG. 2) to move the movable roller 8c upward toward the stationary roller 8b for retaining the movable roller 8c between the stationary roller 8b and an inner surface of the hollow seat 8a, thereby clamping the pull ropes 6 between the stationary roller 8b and the movable roller 8c. To raise the slats 5, the pull ropes 6 are pulled downwardly. At this time, the movable roller 8c is permitted to move downwardly away from the stationary roller 8b. When the slats 5 are raised to a desired position and are to be positioned thereat, the pull ropes 6 are moved rightward to move the movable roller 8c upwardly for clamping the pull ropes 6 between the stationary roller 8b and the movable roller 8c. Since the pull ropes 6 are kept in rolling contact with the periphery of the stationary roller 8b during operation thereof, the pull ropes 6 can be operated in a relatively smooth manner. However, during operation of the pull ropes 6 for raising and lowering the slats 5, a relatively large amount of space around the Venetian blind is required for rightward and leftward movement of the pull ropes 6. Moreover, in the aforementioned conventional Venetian blind, the tilt control unit 9 for controlling tilting of the slats 5 is separate from the clamping unit 8 for controlling raising and lowering of the slats 5. The conventional Venetian blind is thus inconvenient to operate and has a disorderly appearance.
Referring to FIG. 3, a conventional operating device which combines the functions of controlling raising and lowering of the slats and adjusting tilting angle of the slats in a single structure is shown to comprise an elongated operating rod which includes a tubular connector 11a that is exposed from a top housing of a Venetian blind to which the operating device is applied, and that is coupled to a tilt control unit 11 for adjusting tilting of the slats (not shown) of the Venetian blind. The operating rod further includes an elongated sleeve 12 which has an upper end connected pivotally to a lower end of the tubular connector 11a such that axial rotation of the elongated sleeve 12 results in corresponding axial rotation of the shaft of the Venetian blind by means of the tilt control unit 11 so as to tilt the slats of the Venetian blind. Pull ropes 13 of the Venetian blind pass through the tubular connector 11a and the elongated sleeve 12. A retaining unit 14 is provided at a lower end of the elongated sleeve 12 and includes a positioning tube 14a, a biasing spring 14b, a retaining member 14c, an outer sleeve 14d and a retaining piece 14e. The pull ropes 13 extend out of the elongated sleeve 12 and pass through the positioning tube 14a. The biasing spring 14b biases the outer sleeve 14d upwardly so that the pull ropes 13 are clamped tightly between the retaining member 14c and the positioning tube 14a. The outer sleeve 14d is movable downwardly relative to the elongated sleeve 12 to compress the biasing spring 14b so as to release the pull ropes 13 and permit raising and lowering of the slats.
The aforementioned operating device offers the advantage of combining the functions of controlling raising and lowering of the slats and adjusting the tilting angle of the slats in a single structure. However, the clamping effect provided by the operating device for clamping the pull ropes is unsatisfactory. It is desirable to incorporate a clamping unit of the type shown in FIG. 2 in an elongated operating rod to achieve a better pull rope-clamping effect, while maintaining the advantage of combining the two different functions in a single structure.
U.S. patent application Ser. No. 08/844,406 by the Applicant discloses an operating device for a Venetian blind. The operating device includes a rotary tilt control unit adapted to be coupled to the shaft of the Venetian, a positioning tube connected to the tilt control unit and adapted to permit extension of the pull ropes of the Venetian blind therethrough, a retaining member axially movable in the positioning tube and having a tapered upper end portion, a biasing spring disposed in the positioning tube for biasing the retaining member upwardly so that the pull ropes can be clamped between the tapered end portion of the retaining member and a top wall of the positioning tube, and an elongated sleeve disposed around the positioning tube and associated operably with the retaining unit so that the pull ropes are released from the retaining unit when the elongated sleeve is moved downwardly. Improvement is desired in the aforementioned operating device to provide a better clamping effect for clamping releasably the pull ropes.